Characteristics and risk assessment of thermal pollution from stormwater runoff in urban lake

Urban expansion has led to changes in land use patterns, with the increased urban surface area replacing natural infiltration channels for stormwater. This can contribute to higher water temperatures of recipient water bodies, thus reducing the quality of aquatic ecosystems. Current research primarily focuses on the impact of thermal pollution on aquatic organisms and the effectiveness of low-impact development facilities in controlling thermal pollution. However, there is a lack of research addressing the capacity of water bodies to handle heat loads and control thermal pollution. This paper monitored the current thermal pollution of the underlying surface in the study area, and the characteristics of thermal pollution change at different periods of 6 h were analyzed. Additionally, a mathematical model was developed to incorporate the new parameter of lake thermal load carrying ratio (LTR) into the design of the Sponge City Renovation. The results showed that although the highest event runoff mean temperature was observed for rainfall events during the afternoon period, the total runoff thermal load was highest during the early morning period. The maximum LTR reached 145 % for the lake. Based on the LTR parameter to calculate the scale of plot modification, 16 % of the concrete underlayment in the Daxing campus can be modified into green space with the addition of 14,180 m2 of bioretention facilities, which can effectively reduce the LTR value by up to 48 %, at which time the water body will no longer be exposed to the risk of thermal pollution. The LTR index can be utilized in low-impact development and renovation projects to effectively assess the thermal pollution risk of stormwater runoff generated by plots. This assessment holds high practical value for evaluating the environmental impact of such developments.